The role of onium salts in the oxidation of hydrocarbons by O2 catalysed by cationic phase-transfer reagents

Abstract

Experimental and theoretical evidence is presented that cationic phase-transfer catalysts promote the homolytic decomposition of hydroperoxide initiators into radicals, this being a fundamental step in the catalysis of the oxidation of hydrocarbons bySuch decomposition of the model substance tert-butylwas found to have a value of 2, independently of the nature of the /*O 2 counteranion present. It is assumed that the interaction between hydroperoxide and onium cation is mainly electrostatic in nature and that its e †ectivity depends on the positive charge density on the onium cation, which is controlled by the nature and dimensions of the counteranion. The role of water in the decomposition of t-BHP is also elucidated.

Selective Catalytic Oxidation of CH Bonds with Molecular Oxygen

“…A further aerobic oxidation combines NHPI, xanthone and Me 4 NCl as a catalyst that warrants a fast decomposition of the alkylhydroperoxide 55. 56 Recently, a V‐catalyzed aerobic alkane oxidation using carboxylic acids and Eu(OTf) 3 as cocatalyst was reported 57…”

Selective decomposition of cyclohexyl hydroperoxide by copper ion-containing quaternary ammonium salts in alkali-free medium

“…This result was consistent with other previous research. [18,28,29] What's more, radicals that formed by the homolytic activation of CHHP might be stabilized by BHT radical. The structures of the corresponding free radicals formed in chain initiation were studied by GC-MS preliminarily (Fig.…”

The Role of Onium Salts in the Pro‐Oxidant Effect of Gold Nanoparticles in Lipophilic Environments

“…The ability of TOAB and of other onium salts to act as autoxidation initiators in the presence of hydroperoxides in apolar solvents was first recognized by Bredereck et al . and then confirmed by others . Kasaikina et al.…”

“…studied the decomposition of t BuOOH induced by surfactants and reported that the catalytic activities depend on the nature of both the cation and the counterion. With tetrahexylammonium salts, for instance, the efficiency was found to decrease in the order Br − >SCN − >Cl − >NO 3 − >ClO 4 − >F − . The activities of different ammonium ions, having Cl − as counterion, decreased in the order Hex 4 N + >BzBu 3 N + >MeOct 3 N + >Me 4 N + (Hex=hexyl, Bz=benzyl, Oct=octyl) .…”

“…With tetrahexylammonium salts, for instance, the efficiency was found to decrease in the order Br − >SCN − >Cl − >NO 3 − >ClO 4 − >F − . The activities of different ammonium ions, having Cl − as counterion, decreased in the order Hex 4 N + >BzBu 3 N + >MeOct 3 N + >Me 4 N + (Hex=hexyl, Bz=benzyl, Oct=octyl) . Analysis of the products formed after mixing t BuOOH with various onium salts at 70 °C in chlorobenzene revealed the formation of t BuOH, O 2 , and t BuOO t Bu, which are fingerprints of a radical‐chain mechanism having t BuO .…”